Maximum Stress Theory Research Articles

Bending of fusion-bonded thermoplastic single lap joints

The assembly of thermoplastic composites is one of the most important issues for their reliable use in the aerospace and automotive industries. Assembly through co-curing is a process that enables simultaneous bonding and curing of adherends and is a preferable option for these industries. This paper presents a study of fusion-bonded, co-cured single lap joints with thermoplastic adherends that were subjected to four-point bending. Processing of the joint created a 45° notch at one edge of the overlap. The effect of this notch on the strength of the joint was assessed in tension and compression by flipping the joint. Compared to samples without such notches, experiments indicated that the tensile stresses in the vicinity of the notch decreased the maximum load and applied displacements at failure initiation by about 30 % and 33 %, respectively. In order to better understand this behavior, the joints were also analyzed using finite element simulations. The initial failure was predicted using the Maximum Stress Theory. Both experimental and numerical results were consistent up to the initial failure. The analysis did not account for the subsequently observed interlaminar delamination in the adherends. This type of failure would most likely be approached using measured interlaminar traction-separation relations in a cohesive zone modelling approach.

Mixed mode I/II and I/III fracture toughness investigation for preplaced aggregate concrete mixtures: Experimental study and theoretical prediction

AbstractIn this paper, mixed mode I/II and I/III fracture toughness of preplaced aggregate concrete was studied using an edge‐notched disc bend specimen. The results showed the dependency of the fracture toughness value on the mode mixity. The values of modes I, II, and III fracture toughness were obtained to be equal to , , and , respectively. Several theoretical fracture criteria were examined for predicting the trends of experimental data in the tested preplaced aggregate concrete material. The 3D averaged strain energy density criteria provided the best predictions for the KIIIc/KIc ratio. Mixed mode I/III fracture toughness data were between the predicted envelopes of the maximum tensile stress and 3D maximum tangential strain theories. The generalized maximum tangential stress criterion provided accurate predictions for pure mode II and mixed mode I/II fracture data among the investigated mixed mode fracture criteria. By comparing the preplaced aggregate concrete fracture results with those of other types of concrete, it is observed that preplaced aggregate concrete has acceptable and in‐the‐range fracture resistance.

Composite Plate Optimization: Integrating Analysis Techniques and Design Iterations for Enhanced Mechanical Performance

This essay delves into the comprehensive analysis of composite plate behavior under various loading conditions, focusing on uniaxial loading and the effects of layup design on safety factors. Through a comparative study between Classical Laminate Plate Theory (CLPT) calculations and Finite Element (FE) analysis, discrepancies in stress and strain predictions are identified, attributing them to assumptions made in each method. Furthermore, the essay explores failure prediction using Tsai-Wu criteria and Maximum Stress theory, determining the safety of laminates under different loading scenarios. Additionally, Finite Element analysis is employed to assess the impact of layup design variations on safety factors, leading to recommendations for optimized designs. The limitations of FE models compared to physical tests are discussed, along with alternative approaches such as advanced manufacturing techniques and novel fiber architectures to further enhance safety factors and alter failure modes.

A Robust Adaptive Mesh Generation Algorithm: A Solution for Simulating 2D Crack Growth Problems.

This paper introduces a robust algorithm that efficiently generates high-quality unstructured triangular meshes to model complex two-dimensional crack growth problems within the framework of linear elastic fracture mechanics (LEFM). The proposed Visual Fortran code aims to address key challenges in mesh generation including geometric complexity, required simulation accuracy, and computational resource constraints. The algorithm incorporates adaptive refinement and updates to the mesh structure near the crack tip, resulting in the formation of rosette elements that provide accurate approximations of stress intensity factors (SIFs). By utilizing the maximum circumferential stress theory, the algorithm predicts the new crack path based on these SIFs. Throughout the simulation of crack propagation, a node splitting approach was employed to represent the progression of the crack, while the crack growth path is determined by successive linear extensions for each crack growth increment. To compute stress intensity factors (SIFs) for each increment of crack extension, a displacement extrapolation method was used. The experimental and numerical results demonstrated the algorithm's effectiveness in accurately predicting crack growth and facilitating reliable stress analysis for complex crack growth problems in two dimensions. The obtained results for the SIF were found to be consistent with other analytical solutions for standard geometries.

Mechanical characterization of intermittent weak interlayer based on DIC and acoustic emission technique

Current research on intermittent structural surfaces tends to concentrate on intermittent joints, often neglecting the abundance of intermittent weak interlayers present in rock structures. To analyze the effect of intermittent weak interlayer on the mechanical properties of rock mass, specimens with varied interlayer thickness and dip angles were prepared and subjected to uniaxial compression tests using an acoustic emission system and Digital Image Correlation (DIC) technique. The results revealed an inverse relationship between the interlayer thickness (t) and dip angle (θ), and the uniaxial compressive strength. Through a nonlinear fitting method, an empirical strength equation for these interlayers was established. Acoustic emission (AE) counts and cumulative acoustic emission counts increased with loading, and the RA-AF values indicated that the specimens were dominated by shear damage, and the larger the thickness and dip angle of the interlayer, the higher the proportion of shear damage. In terms of failure mode, the greater the thickness of the interlayer, the lower the level of development of cracks other than the main crack, and the greater the dip angle of the interlayer, the fewer the number of wing cracks required for specimen failure and the lower the degree of wing crack development. The increase in interlayer thickness and dip angle resulted in a specimen structure that was more susceptible to damage. The actual crack initiation angles agree with the theoretically calculated angles based on the maximum tensile stress theory. These findings emphasize the critical role of these parameters in influencing the failure mode of rocks.

Numerical and Experimental Analysis to Predict the Compressive Strength of Pristine Composite Laminates

In this work, the numerical and experimental work has been carried out to verify the compressive strength of pristine composite laminates. Theoretical computations have been carried out using MATLAB to compute the strength and buckling load. Finite Element Analysis has been carried out for the composite laminate using two and three dimensional elements. PATRAN as the Pre and Post processing package and NASTRAN as the solver have been used in this work. The various failure theories considered in this article are Tsai-Wu, Hill, Hoffman, Maximum Stress and Quadratic failure theory (YSFT). All the first four failure theories are available as a standard criterion in the PATRAN package. The fifth quadratic failure criterion has been implemented using PATRAN Command Language. Static analysis along with failure theories has been carried out to compute the strength of the laminate. Static and buckling analysis has been presented for both in two-and three-dimensional models. Experiments have been carried out on number of pristine laminates and the strain values obtained from FEA have been compared with the experimental values. The theoretical computation provides a load value which is about the elastic limit of the specimen. It is generally observed that quadratic failure theory (YSFT) provides least failure indices and may be employed for conservative design.

Particle-based numerical simulation of continuous ice-breaking process by an icebreaker

The continuous ice-breaking capacity of an icebreaker is an important indicator of its efficiency. The ice resistance encountered by an icebreaker has a significant influence on its continuous ice-breaking capacity. In this study, we develop a numerical model based on the moving particle semi-implicit (MPS) method, which is a particle method based on continuum mechanics, for predicting the ice resistance encountered by icebreakers during continuous ice-breaking operations. Before fracture, the ice is assumed to be a linear elastic material, and the maximum tensile stress theory is used as the fracture criterion. A scalar function composed of the first principal stress gradient and the first eigenvector of the stress tensor is introduced to express the relative positions of the new crack and corresponding particle pair. As the hull is represented by polygons and the ice fragments are represented by particles, the collision points between the hull and the ice, i.e., between polygons and particles, is determined using a novel search algorithm that expands a cell linked-list algorithm. The collisions between individual ice fragments and between the hull and an ice fragment are considered using a particle-based model that is a modified form of the Hertz contact model. The proposed algorithm was verified using experimental data obtained from three-point bending tests on model and freshwater ice specimens that were performed by the Korea Research Institute of Ships and Ocean Engineering (KRISO) and Korea Maritime and Ocean University (KMOU), respectively. The verification process revealed that the closer the properties of the ice to the linear elastic properties assumed in the numerical model, the higher the accuracy of the proposed algorithm. The verified algorithm was used to predict the ice resistance encountered by a model icebreaker during a continuous ice-breaking process. A series of convergence and parametric tests were performed for the main parameters of the continuous ice-breaking simulation, and the experimental results obtained by KRISO were used for comparison. The maximum relative errors from experiment were approximately 12% and 30% under free (Fr) and semi-fixed (SF) side boundary conditions, respectively. The proposed numerical algorithm can successfully predict the ice resistance encountered by an icebreaker and the occurrence of near- and far-field fractures during a continuous ice-breaking process.

Reliability Study of Wood–Plastic Composites Based on Probabilistic Finite Elements

In order to further expand the application field of wood-plastic composites, it is necessary to study the reliability of this material in practical applications. Therefore, this work takes the maximum stress theory as the failure criterion and uses the finite element method to simulate the reliability of the WPC specimen. Based on the simulation results, the relationship between reliability and random variables such as geometric parameters and external load is analyzed. Finite element simulations are carried out for each group of specimens under the same operating environment to analyze the influence of process parameters such as the wood flour content, granulation temperature, coupling agent content and screw speed on the reliability of the specimens during the manufacturing process. The results show that the wood flour content has the greatest influence on the reliability of the specimens when the wood-plastic composites are used as building paving materials, followed by the granulation temperature, coupling agent content and screw speed, which provides a basis for the selection of the manufacturing process parameters of WPC based on reliability.

The effects of open hole and fiber orientation on Kevlar/Epoxy and Boron/Epoxy composite laminates under tensile loading

Software simulation is the most effective way of visualizing the deformation and stress of materials or structures and hence predicting the maximum force that can be applied before failure or rupture. This paper aims to study the effect of round cut outs on Kevlar/Epoxy and Boron/Epoxy with three fiber orientations using ANSYS. The work is conducted in three stages, mesh convergence analysis, numerical validation of the software used and failure analysis. Failure analysis is conducted by using the finite element method (FEM) with Maximum stress theory as the failure criteria. The results show a significant difference of strength between solid and open hole composite laminates, in which there is a 90% or more reduction in strength for both epoxy laminates. Among Kevlar/epoxy and boron/epoxy, boron/epoxy showed higher tensile failure either in solid or in the lamina with open hole. The direction of fiber orientation also does affect the failure behaviour of the composite laminates. Hence, it is proven that the current study is important in understanding the failure behaviour of the composite plate in which can be useful in contributing the knowledge of these laminates for further study.

Adaptive Finite Element Modeling of Linear Elastic Fatigue Crack Growth.

This paper proposed an efficient two-dimensional fatigue crack growth simulation program for linear elastic materials using an incremental crack growth procedure. The Visual Fortran programming language was used to develop the finite element code. The adaptive finite element mesh was generated using the advancing front method. Stress analysis for each increment was carried out using the adaptive mesh finite element technique. The equivalent stress intensity factor is the most essential parameter that should be accurately estimated for the mixed-mode loading condition which was used as the onset criterion for the crack growth. The node splitting and relaxation method advances the crack once the failure mechanism and crack direction have been determined. The displacement extrapolation technique (DET) was used to calculate stress intensity factors (SIFs) at each crack extension increment. Then, these SIFs were analyzed using the maximum circumferential stress theory (MCST) to predict the crack propagation trajectory and the fatigue life cycles using the Paris' law model. Finally, the performance and capability of the developed program are shown in the application examples.

Progress in the engineering design of ITER Langmuir probe

High heat flux reaching 10 MW/m2 can be foreseen for the ITER (International Thermonuclear Experimental Reactor) divertor, which is also defined as the designed heat flux for ITER Langmuir Probes because the probes are directly attached on the side of divertors. Such high heat flux induces a high temperature environment and consequent high thermal stress, yet there is no dedicated cooling for the probe structure. A new DLP (Divertor Langmuir probe) design which is called “full-tungsten design” has been proposed for this harsh environment. Alumina is used as the electrical insulating material, which is a kind of brittle material and very easy to generate crack, especially when considering its strength would be decreased due to the elevated temperature.To assess compliance with the heat loads, the probe and environment are simulated using software ANSYS by finite element method. The full-tungsten DLP structure shows good thermal and mechanical behaviors under the specified cyclic thermal loads. Transient thermal analysis combined with elasto-plastic analysis has been performed, the thermal analysis result shows the materials temperature is acceptable. Damages due to progressive deformation as well as time-independent fatigue have been assessed according to the structural design criteria SDC-IC (The Structural Design Criteria for ITER In-vessel Components). Damage on alumina layer due to fast fracture has also been assessed based on the maximum tensile stress theory. The analysis results show the design is quite promising.

Uniform fatigue characterization of high modulus asphalt mixtures under three-dimensional stress state

To improve the durability of asphalt pavement, high modulus asphalt mixtures were developed and widely utilized to construct heavy trafficked pavements to resist rutting. Except for rutting, serving under repeated heavy loads, pavements with high modulus asphalt mixtures are also vulnerable to fatigue cracking. To prevent fatigue cracking, the fatigue resistance of high modulus asphalt mixtures is a crucial indicator for pavement structural design and checking computations, which is generally obtained by laboratory tests. However, the current test methods are generally based on maximum tensile stress or strain theory and neglecting the effects of loading velocities, so the fatigue resistance obtained cannot match that under actual pavement serving conditions. Moreover, the fatigue performance of high modulus asphalt mixtures obtained by different test methods are quite different, which caused random and disunity when selecting fatigue parameters for pavement structural design. Therefore, the objective of this paper is to accurately and uniformly characterize the fatigue resistance of high modulus asphalt mixtures. To this end, the indirect tensile, direct tensile, unconfined compressive strength and fatigue tests of high modulus asphalt mixtures were implemented under distinct loading velocities. Based on the Desai yield criterion, the strength yield surfaces under diverse loading velocities and the fatigue path of high modulus asphalt mixtures in three-dimensional stress state were established. Finally, the fatigue life values of high modulus asphalt mixtures obtained under distinct test methods and loading velocities were uniformly characterized by the relationship between fatigue life and equivalent stress ratioΔ, which wasNf=Δ-5.42. With the uniform characterizing model, the disunity of fatigue parameters can be eliminated, and the fatigue resistances of high modulus asphalt mixtures under three-dimensional stress states and different loading velocities can be evaluated.

Compressive Failure Behaviour of Kevlar Epoxy and Glass Epoxy Composite Laminates Due to the Effect of Cutout Shape and Size with Variation in Fiber Orientations

The increasing trendof constructing componentsmade of composite laminates is due tothe flexibility intailoring their properties and high strength-to-weight ratio. Nevertheless, most practical components involve cutout features for fastening and these cutouts could significantly reduce the strength of the laminate. Due to its importance, many studies were conducted to study the effect of circular cutouts however, there is lack of information regarding the effect of various cutout shapes. Therefore, this study aims to investigate the compressive failure behaviour of Kevlar Epoxy and Glass Epoxy composite laminates due to different cutout shapes and sizes with variation in fiber orientations. Finite element software, ANSYS were used to simulate the deformation and failure behaviour of the laminates under compressive load. Prior to that, mesh convergence analysis and numerical validation were performed. Failure analysis was conducted for various cutout shapes (square cutout, diamond cutout, and circular) and size, based on Maximum Stress Theory. The results show that the existence of the cutouts on the composite laminates have reduced up to ten times the strength of the laminated composite plates. This information regarding the failure behaviour is important when designing components made of composite laminates under compression.

Microstructural damage and response of stiffened composite submersible pressure hull subjected to underwater explosion

ABSTRACT Submerged structures in naval applications are susceptible to underwater explosion and predicting the transient response and damage is a prime concern for the designer. Coupled Arbitrary Lagrangian-Eulerian (ALE) based numerical investigation using LS-DYNA for the inelastic dynamic response and microstructure failures of composite hull subjected to UNDEX is presented. As a prelude to the study, shock pressure in fluid domain and strain values obtained on the composite pressure hull is compared with that available in literature. The numerical study is extended to predict the large deformation, puncture and microstructural behaviours of the hull by varying the charge weight of the explosive. The results of the predicted large deformation, puncture of the hull and the microstructural failures such as fibre tension, fibre compression, matrix shear, matrix tension, and matrix compression based on the Chang- Chang composite failure model, Tsai-Wu failure theory and maximum stress theory are presented.

Initiation and Fracture Characteristics of Different Width Cracks of Concretes under Compressional Loading

A stress concentration at a crack tip may cause fracture initiation even under low-stress conditions. The maximum axial stress theory meets the challenges of explaining the fracture propagation of a non-closed fracture of cracked concretes under compressional loading. Uniaxial loading tests of single-crack concrete specimens were carried out and a numerical simulation of fracture propagation under uniaxial compression was performed. The radial shear stress criterion for a mode-II fracture is proposed to examine the stress intensity factor (SIF) of the pre-crack specimens under compressional loading. When the maximum radial shear stress at the crack tip is larger than the maximum axial tensile stress, and the maximum dimensionless SIFs can satisfy frθmax/fθmax > 1 and frθmax/fθmax > KIIC/KIC (fθmax=KIe/σyπa and frθmax=KIIe/σyπa are maximum dimensionless mode-I and mode-II SIFs, respectively), the crack will extend along the direction of the maximum radial shear stress. The influence of the single-crack angle and width on the mechanical properties of the specimens was examined. The experimental and numerical results indicate that the existence of cracks can considerably weaken the strength of the specimen. The distribution and width of the cracks had a significant effect on the specimen strength. The strength of the concrete specimen initially decreased and then increased with increasing fracture angle. The failure mechanism and rupture angle of pre-crack brittle material while considering crack width will be discovered.

Properties and performance index of natural fiber reinforced cross-ply composites made from Dioscorea alata stem fibers

In this study, post-harvest Dioscorea alata stem fiber was rated, extracted and treated with 2 % concentration of Sodium hydroxide (NaOH) for 4 h. Three replicate samples of Dioscorea alata stem fibre/epoxy composites (DASFEC) were prepared as per ASTM D3039 and tested under tension with a crosshead displacement rate of 2 mm/min. The laminate in-plane strains (ex0,ey0,eyx0), out-plane strain due to the bending with the curvatures (kx, ky, kxy), strains (ex, ey, exy) and ply stresses in material axes (σ1, σ2, τ12) were calculated using Classical Laminate Theory. The longitudinal tensile strength, yield strength, shear strength and Elastic modulus of Dioscorea alata stem fiber/epoxy lamina (DASFEL) were respectively estimated as 94.2 MPa, 44.4 MPa, 18.1 MPa and 3552.5 MPa. Fourier Transform Infrared Spectroscopy (FTIR) Analysis captured the O-H present in cellulose II at 2750.3 cm−1, 3001.3 cm−1, 3279.849 cm−1and 3813.16 cm−1 peaks with weak intensity on the average. Energy-Dispersive X-ray Spectroscopy (EDS) analysis showed the high presence of Carbon (C) and Oxygen (O) with small deposit of Silicon (Si). The damage onset for individual ply was detected by both Maximum Stress Theory and Tsai-Hill Theory in ply 2 at 90 degrees while the overal laminate strenght (σx) was estimated as 64.7 MPa. The study established that DASFEC is desirable for car interior panel design.

Failure analysis of simple overlap bonding joints and numerical investigation of the adhered tip geometry effect on the joint strength

Abstract This study was carried out in two stages. In the first step, a numerical study was performed to verify the previous experimental study. In accordance with the previous experimental study data, single lap joints models were created using the ANSYS finite element analysis program. Then, nonlinear stress and failure analyses were performed by applying the failure loads obtained in the experimental study. The maximum stress theory was used to find finite element failure loads of the single lap joints models. As a result of the finite element analysis, an approximate 80 % agreement was found between experimental and numerical results. In the second step of the study, in order to increase the bond strength, different overlap end geometry models were produced and peel and shear stresses in the adhesive layer were compared according to the reference model. As a result of the analyses, significant strength increases were calculated according to the reference model. The strength increase in model 3 and model 5 was found to be 80 % and 67 %, respectively, relative to the reference model.

Application of the Modified Mohr–Coulomb Yield Criterion in Seismic Numerical Simulation of Tunnels

To solve the classical problem that the Mohr–Coulomb yield criterion overestimates the tensile properties of geotechnical materials, a modified Mohr–Coulomb yield criterion that includes both maximum tensile stress theory and smooth processing was established herein. The modified Mohr–Coulomb constitutive model is developed using the user-defined material subroutine (UMAT) available in finite element software ABAQUS, and the modified Mohr–Coulomb yield criterion is applied to construct a numerical simulation of a shaking table model test. Compared with the measured data from the shaking table test, the accuracies of the classical Mohr–Coulomb yield criterion and the modified Mohr–Coulomb yield criterion are assessed. Compared to the shaking table test, the classical Mohr–Coulomb model has a relatively large average error (−6.98% in peak acceleration values, −8.47% in displacement values, −23.93% in axial forces), while the modified Mohr–Coulomb model has a smaller average error (+2.71% in peak accelerations value, +3.19% in displacements value, +7.56% in axial forces). The results of numerical simulation using the modified Mohr–Coulomb yield criterion are closer to the measured data.

Compressive failure behaviour of glass epoxy and graphite epoxy composite laminates due to the effects of different cut-out sizes and variations in fibre orientation

Composite laminates consisting epoxy are widely used in major industries. Hence, the mechanical property of these materials needs to be fully understood. Currently, there is limited studies on the effect of various square cut-out sizes related to glass epoxy and graphite epoxy composite laminates, therefore, the behaviour of these laminates is not fully understood. This paper aims to study the effect of the square cut-out sizes on the failure performance of glass epoxy and graphite epoxy composite laminates with various fibre orientations. Prior to the compressive failure analysis, convergence and numerical validation were conducted. The failure analysis is conducted by using the finite element method (FEM) using ANSYS with maximum stress theory as the failure criteria. The results show a substantial difference in the strength of the laminates without and with cut-outs. The main finding that can be deduced from the study is, the presence of cut-out reduces the strength of the composite laminates. Different fibre orientations effected graphite epoxy composite laminate at a considerable amount compared to glass epoxy laminates. From the results, it is proven that the present study is important in understanding the compressive failure behaviour of the composite plate in which can be useful in contributing the knowledge for further study.

Crack evolution law and failure mode of red sandstone under fatigue–creep interaction

AbstractTo explore the fracture characteristics of rock under the interaction of fatigue load and creep load, fatigue–creep interactive loading experiments were performed on red sandstone with prefabricated cracks. The crack evolution process and failure mode were analyzed using acoustic emission technology and digital image correlation. The results showed that crack growth mainly occurred in the fatigue loading stage; the crack evolution of the sample could be divided into three stages: nucleation and initiation ( ), stable expansion ( ), and unstable fracture ( ). There were distinct differences in the crack propagation modes of the rock samples with different prefabricated crack angles. The relationship between the crack initiation angle and prefabricated crack angle was analyzed based on the maximum circumferential stress theory. Moreover, with an increase in the prefabricated crack angle, the rock sample gradually changed from compression–shear failure to tension–shear failure.